Add missing changelog for ARIA (#4959)

Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
diff --git a/ChangeLog.d/aria.txt b/ChangeLog.d/aria.txt
new file mode 100644
index 0000000..280a7c9
--- /dev/null
+++ b/ChangeLog.d/aria.txt
@@ -0,0 +1,3 @@
+Features
+   * Add PSA API definition for ARIA.
+